This grant will support the continued development of a Human Twin Panel at the Medical College of Virginia that will be a resource at this institution for a wide variety of clinical studies. The genetic control of continuously distributed metric traits will be investigated using a new model for the analysis of quantitative inheritance that involves the study of the descendents of monozygotic twins. The model will be extended to qualitative traits in a collaborative study, with scientists at the University of Oslo in which reproductive histories will be obtained from a estimated 8000 monoygotic twin pairs in the Norwegian Twin Registry. New born twins will be identified and studied in a systematic manner to search for evidence of polar body twinning and superfetation and to measure the significance of placental difference in twins.